Charge boat for volatilization



May 29, 1956 Filed Sept. 9, 1944 R. KROHN 2,747,972

CHARGE BOAT FOR VOLATILIZATION 2 Sheets-Sheet l 2 Sheets-Sheet 2 May 29,1956 .R. KROHN CHARGE BOAT FOR VOLATILIZATION Filed Sept. 9, 1944INVENTOR. Roy )frohn CHARGE BOAT FQR VOLATILIZATIQN Roy Krohn, Berkeley,Calif., assignor to the United Statesof America as represented by theUnited States Atomic Energy Commission This invention relates toimprovements in sublimation apparatus and processes for thevolatilization of chemicaI materials. More particularly this inventionconcerns improvements in charge boats and procedure for volatilizingchemical materials in sublimation processes, especially uraniumcompounds, exemplified by certain. halogen derivatives of uranium. Theinvention constitutes an improvement over the inventions disclosed in U.S. Patent applications, Serial No. 552,556, filed September 2, 1944, nowPatent No. 2,574,842, and Serial No. 552,557, filed September 2, 1944.

In companion application Ser. No. 553,446 filed September 9, 1944, inwhich I am a joint inventor, it is indicated that a number ofsublimation processes and apparatus have been described in the priorart. Said companion application concerns a novel sublimation apparatusand process having advantages over the prior art.

In the present application there are described certain improvementfeatures which may be employed in sublimation apparatusconstructions ofthe type described in the companion application aforementioned as wellas novel features ofconstruction which may be utilized in sublimationapparatus generally or in related fields.

I have found that there are improvements which may be made inthe devicesor units used for holding the chemical materials to be volatilized andin related parts whereby volatilization is quicker, separation betterand other advantages obtained. In further detail I have provided animproved construction of the charge holding means, referred to herein asa charge boat, which construction is particularly useful in thevolatilization of certainuraniurn halides for obtaining better chargedistribution and accelerated volatilization.

This invention has for one object to provide improvements in sublimationapparatus and processes.

Another object is to provide an improved construction for the chargeholding and volatilizing device referred to herein as a charge boat.

I Still another object is to provide a charge boat construction in whichthere may be obtained better charge distribution and acceleratedvolatilization.

Another object is to provide a charge boat construction that: isparticularly useful in methods of processing uranium materials.

- Stilbanother object is to provide a boat construction that facilitatesthevolatilization and separation of mixed halide. compounds.

Another" object is to provide a process for the rapid volatilization ofchemical materials.

- Another object is to provide a method of volatilizationapplicablextothe processing of uranium halide materials to;UCl'e andUCl4.

. Atstillfurther object is to provide a process in which theremay besimultaneous separation and crystallizing stepsiappliedtto.uraniumhalides.

Qthervobj'ects: will appear hereinafter.

I have found that improved operation in sublimation V .processesfmay beobtained bymeans of employing a 2,747,972 Fatented May 29, 1956 chargevolatilizing device comprising an elongated boat construction having anumber of trays or shelves therein.

For a further understanding of my invention, reference is made to theattached drawing forming a part of the present application.

Fig. 1 is a semi-diagrammatic side elevation view of a sublimationapparatus in which certain parts have been shown broken away and otherparts shown in section. In this figure the general relationship andpositioning of my improved charge boat in a sublimation apparatus isindicated;

Fig. 2 is a sectional view taken on the line AA of Fig. 1 showingcertain of the related parts in a sublimation unit of a type in which ithas been found advantageous to use my charge boat.

Fig. 3 is a sectional view on enlarged scale, taken on the line BBof-Fig. 1, showing the positioning of my charge boat within thesupporting member therefor.

Fig. 4 isla detailed view of the inner shelf or tray portion of thecharge boat construction of the present invention.

Fig. 5 is a detailed view, on enlarged scale, showing the outer portionof the charge boat construction.

In order to provide a better understanding of the environment andconditions under which the improved charge boat of the present inventionmay be used, there is briefly described ahorizontal sublimationapparatus of a type in combination with which theuse of the novel chargeboat of the present invention has been found particularly satisfactory.Following the general description of the sublimation equipment, detailsconcerning the improved charge boat of the present invention are setforth.

Referring now to Fig. 1 concerning a sublimation apparatus, referencenumeral 2 represents a movable electric furnace. The furnace may be ofconventional construction'including heating elements 3, insulation 4,and various other usual parts for the construction and operation ofelectric furnaces. Wheels 6 which move on track- 7 may be provided forpermitting the movement of the furnace into and out of heating position.That is, the furnace may be moved out of position for cooling, repair,and other similar action as respects the apparatus.

As-may be seen in the drawing, the furnace is adapted to-move onto andinclose an elongated hollow member 8 which member houses the charge boat9 of the present invention, the latter being better shown in Figs. 3, 4and 5. Member 8 is connected to, and projects horizontally outwardlyfrom, a condenser structure 11, better shown in Fig; 2, such that theinterior of the hollow member 8 communicates with the interior ofcondenser 11.

The condenser 11 is connected by means of conduit 12 to a vacuum system(not shown). The particular vacuum system employed for reducing thepressure on the condenser and charge boat, and for removing air whichmight cause oxidation, is not a limitation on the present invention. Ingeneral, means for obtaining reduced pressure less than 50 millimetersof mercury would be employed in conducting the sublimation process.

Referring now to Fig. 2, the condenser includes an inner liner 21disconnected from the outer shell 22. After removing the condenserclosure 24 (see Fig. l), the entire'liner 21 maybe pulled out of theapparatus. The outside of the condenser is provided with a number ofcooling coils 23 of conventional design which may be connected. towater. lines or other cooling medium by means of detachable connections.

Within the liner 21 but attached thereto is the convolute' or: spiralmetallic member 26. This member functions to cause the. vapors from thevolatilization in: the charge boat construction of the present inventiontomove in an elongated spiral path. Also the metal member 26 functionsas a condenser surface as will be further described under the operationof the equipment.

The liner 2.1 fits within the apparatus against boat 9 in asubstantially vapor tight manner by means of the interposed sealing ring7. This ring 27 is similar to an automotive piston ring and by expandingagainst the interior surface of member 8 gives a vapor tight seal. Thisprevents vapors evolved in the charge boat from penetrating betweenliner 21 and the condenser wall 22. The liner 21 has a removable head 28attached thereto by bolts indicated at 2?.

As stated above, the sublimation apparatus assembly which has beendescribed constitutes one type of arrangement in which my improvedcharge boat may be employed. However, the details of construction of thesublimation apparatus in general are not a limitation on the use of thecharge boat as there are other sublimation apparatus constructions orother devices for similar purposes in which my charge boat may also beused. For

example, reference is made to the sublimation apparatus described incompanion Hecker application, Ser. No. 552,557 filed September 2, 1944.

Considering now in detail the construction of the charge boat with whichthe present invention is primarily concerned, as indicated the chargeboat and its position in a sublimation apparatus has been shown in Fig.1, the boat being indicated by reference numeral 9. The outer portion ofthe boat is better shown in Fig. and is in effect a cylindrical metaltank with a portion cut away as indicated at It). The boat and relatedparts, as the trays or shelves, are preferably constructed from acorrosive and heat resistant alloy. For example, the commerciallyobtainable alloy Hastelloy" may be employed. It has been found thatalloys containing a high content of nickel and chromium, together withsmaller contents of elements such as cobalt, tungsten, molybdenum,manganese and iron constitute satisfactory materials of construction.Since these various alloys may be obtained commercially, furtherdescription is unnecessary.

Referring to Fig. 3 showing the boat construction in section, it will benoted that the boat 9 is supported within and by means of hollow member8. The boat 9 contains the shelf or tray carrying member 31 thatsupports the trays upon which the chemical material to be sublimed isdistributed. That is, a plurality of trays or shelves 35, 36, and 37 areprovided which are hinged to member 31 by means of the hinge and rodconstructions 32, 33 and 34.

The details of the shelf or tray construction may be further observed byreference to Fig. 4 wherein it will be noted that the shelves or trays35, 36, and 37 may be folded up for the purpose of permitting theinsertion of the tray carrying member 31 into the cutaway portion ofboat 9. Suitable cross members 38 may be provided for supporting theshelves or trays when they are opened out into a position for carryingthe material to be volatilized. While the cross member 38 is describedonly in connection with the upper shelf, it may be used for supportingother of the shelves, if desired. The lower shelves, as 36 and 37, maybe notched as indicated at 39 and 4:) to permit the shelves being foldedup without interference from member 38.

It will be noted that the overall length of the trays and associatedparts is less than the length of boat 9. Therefore, when the trays arepositioned within boat 9, there is a space 44 (see Fig. 1) into whichthe vapors from the trays may escape.

In the operation of the apparatus the member 31 is inserted into boat 9by folding up the shelf members 35, 36, and 3'7. After insertion, theshelf members may be successively opened out, and the materials to bevolatilized spread on the surface of the shelves or trays in layers ofthe desired thickness depending upon the par ticular material to beprocessed, the size of the apparatus and related factors. As apparent,the lower shelf, shelf 37, would first have charge distributed thereonbefore unfolding shelf 35. In general the weight of the charge containedin boat 9 may be between to 250 pounds, but this would, of course,depend on the size of the apparatus.

The sublimation apparatus in which my charge boat is to be used, such asthe apparatus shown in Fig. l, is opened. That is, the condenser head 24is removed and the liner and other parts within the apparatus taken out.The boat 9, filled with the charge distributed on the trays 35, 36, and37, is then slid into the hollow member 8 to the back thereof. Thesealing ring 27 is inserted through the front of the apparatus andpushed back into member 8 so that the ring 27 abuts the end of boat 9.The liner 21 is next pushed into place through the front of theapparatus so that it abuts the above-mentioned sealing ring. In thismanner, inasmuch as the ring expands against the member 3, a vapor tightfit to prevent vapors from penetrating between liner 21 and wall 22 isobtained. The liner closure head 23 and condenser head 24 and otherparts are bolted into place, couplings made to the cooling fluidconnections, and other action taken to complete the readiness of theapparatus for operation.

As already mentioned, the charge boat of the present invention is usefulfor processing uranium halides. For example, in converting or separatinguranium halides into UClc and UClr the shelves 35, 36, and 37 would havespread thereover the charge of uranium halides to be sublimed. After thecharge has been distributed in the charge boat as described and theapparatus otherwise assembled, the pressure is slowly reduced to preventany carryover of charge particles through conduit 12. The furnace isrolled into place as shown in Pig. 1 and heat applied to causevolatilization of the charge. The furnace temperatures employed may varyfrom about C. or C. up to several hundred degrees centigrade. The degreeof reduced pressure on the system, as indicated above is generally below50 millimeters of mercury and suflicient at the particular temperatureand other conditions involved to cause sublimation to take place withoutthe formation of a liquid phase. In other words, when processing uraniumhalides as referred to above, it is not desired that liquid uraniumhalides form in the system because of their corrosive action.

After heating under reduced pressure has been accomplished for asufficient period for eliminating entrapped air and the like, thetemperature of heating may be increased to a sufficiently high pointthat the solid charge on the trays is volatilized, vapor passing fromthe trays into space 44, out or" the charge boat through opening 10 intothe interior of the metal spiral 26 and then around the metal spiral.This metal spiral 26 causes the vapors to pass in an elongated pathbefore they can reach the exit conduit 12. During their passage theybecome condensed on the metal spiral 26. This condensation may beobtained by applying suitable cooling to the exterior of the condenser,as for example, a Dry Ice acetone mixture, or part 26 may be cooleddirectly by running suitable cooling conduits thereto. Also, thecondensing temperature may be controlled to some extent by thepositioning of this metal spiral or bafiie 26 at a predetermineddistance from the outer, cooled condenser surface. Since the interior ofthe apparatus is under reduced pressure, the temperature change byconduction is limited. Consequently, the spiral is cooled principally byradiation. However, by the application of a cooling medium such as DryIce and acetone or comparable materials, satisfactory condensingtemperatures may be obtained. By interposing this metal spiral orconvolute 26, practically all of the sublimed product is condensed outso that none passes out of the system through conduit 12.

After the process has continued for a sufiicient period so thatsubstantially all of the sublimable materialin boat 9 under thetemperature and pressure conditions involved, has been volatilized; thefurnace-2 may be rolled olf, and the apparatus permittedto cool;Coolingmay be expedited by introducing, by any-conventionalmeans, a dry,inert gas as nitrogen'within the condenser chamber thereby-providing amedium through which the heat may be transferred by conduction; Afterthe equipment has cooled down suificiently, the condenser head 24 isremoved. The liner 2]. may be pulled out, capped and taken to a dry boxwhere thesublimate may be chipped out and'placed' in suitablecontainers. Inasmuch as the purified sublimed-product is hygroscopic, itis desirable that the material: be maintained in a dry atmosphere.Thereafter the apparatus may be cleanedtas by washing, dried, andanother filled charge boat, ring, and liner inserted, and the processrepeated on another batch of crude material.

I have found that the charge boat and method of volatilization inaccordance with the present invention is particularly. useful in thetreatment of certainuranium halide materials for obtaining. a sublimateofuranium hexachloride. The source of, the materials which'may. betreated, for example, is exemplified by the reaction product. of uraniumoxide with a: clilorinatingmedium such as carbon tetrachloride. Theexactchemicalnature of the uranium chloride obtained. isnot a limitationon the present invention. Such uraniumi chloride materials may comprise,for example, amixtureof uranium hexachloride and uranium tetrachloride..The materials may comprise uranium pentachloride. or materials inwhichthe ratio of uranium to chlorine therein approximates this compound. Orthe uranium materials may include various amounts of all of theaforementioned uranium derivatives, namely, the uranium pentachloride,hexachloride and tetrachloride. Therefore, the charge materials aregenerically referred to herein as uranium chloride materials.

It has been found that such uranium chloride materials may beadvantageously processed by sublimation to obtain uranium hexachloridetherefrom. By means of the excellent charge distribution obtainable onthe tray construction of the present invention, the uranium hexachloridemay be rapidly volatilized even though one-third to two-thirds of thecharged materials may remain on the trays as residue, as for example, asubstantial residual content of uranium tetrachloride. The uraniumhexachloride is relatively more volatile than uranium tetrachloride andmay be sublimed at furnace temperatures between 100 C.200 C. The degreeof reduced pressure utilized during the sublimation is less than 50millimeters of mercury and during the sublimation, a reduced pressure ofthe order of 2 l0 may be employed. The use of reduced pressure removesoxygen, moisture and otherwise eliminates gaseous components which mightcontaminate or exert a destructive influence on the uraniumhexachloride.Also the reduced pressure facilitates the sublimation and preventsformation of the liquid phase.

When such a charge is treated in the apparatus, UCla is driven off invapor form and UCl4 remains as a residue. The UCls is condensed incrystalline form on the spiral 26. Therefore, there is obtainedsubstantially simultaneous conversion or separation and crystallization.By means of the boat construction and charge supporting shelves of thepresent invention the speed of volatilization and acceleration of theconversion or separation of UCls to UCls and UC14 are facilitated.

In a similar manner other materials susceptible of sublimation may berapidly volatilized and processed by utilizing apparatus constructedsuch as described above. Although the charge boat has been shown asheated by an electric furnace, it may be heated by gas heat or othersuitable means. Other changes will be apparent.

It-is to be understood that all matter contained in the abovedescription and examples are to be interpreted asillustrative and'notlimitative of the scope of this invention, and it is intended to claimthe presentinvention as broadly as possible in view of the prior art.

I claim:

1. A sublimation apparatus comprising a chamber having an elongatedheating portion and a condensing portion communicating with said heatingportion, an elongated removable substantially closed containerpositioned within said heating portion, said container having arelatively narrow opening at its top extending along theentire lengththereof, and an elongated tray structure removably positioned withinsaid container, saidtray stmcture having a plurality of normallysubstantially horizontal shelves for supporting portions of a charge tobe sublimed in layers in said heating portion, said tray structureincluding means for pivotally supporting said shelves for rotation aboutrespective axes which parallelthe longitudinal axis of said container,whereby said shelves may be rotated to substantially a vertical positionand the tray structure may thereafter be removed through the opening inthe top of said container.

2; In asublimation apparatus, an elongated substantially closedcontainer having a relatively narrow opening extending along its entirelength at the top thereof, and an elongated tray structure removablypositioned within said container, said tray structure having a pluralityof normally substantially horizontal shelves for supportingindividuallayers of a charge to be sublimed, said tray structure including meansfor pivotally supporting said shelves for rotation about respective axeswhich are-parallel to-thelongitudinal axis of said container, wherebysaid shelves may be collapsed to a vertical position and the traystructure thereafter removed through the opening in the top of saidcontainer.

3. In combination, a substantially closed horizontally disposedcylindrical container, said container having an opening extending alongits top and parallel to its axis, and an elongated tray structureremovably positioned within said container, said tray structurecomprising a vertically disposed support frame, a plurality of normallysubstantially horizontal shelves, and means for pivotally supportingsaid shelves from said frame for rotation about respective axes whichare parallel to the axis of said cylindrical container, each of saidshelves having a width which corresponds to the transverse width of saidcontainer at the particular location of each shelf.

4. A sublimation apparatus comprising a chamber having an elongatedheating portion, an elongated removable substantially closed containerpositioned within said heating portion, said container having arelatively narrow opening at its top extending along the entire lengththereof, and an elongated tray structure removably positioned withinsaid container, said tray structure having a plurality of normallysubstantially horizontal shelves for supporting individual layers of acharge to be sublimed, said tray structure also including means forpivotally supporting said shelves for rotation about respective axeswhich are parallel to the longitudinal axis of said container, wherebysaid shelves may be rotated to a vertical position and the traystructure thereafter removed through the top opening of said container.

5. A sublimation apparatus comprising a chamber having a heating portionand a condensing portion communicating with said heating portion, anelongated removable substantially closed container positioned withinsaid heating portion, said container having a relatively narrow openingextending lengthwise of said container at the top thereof, and anelongated tray structure removably positioned within said container,said tray structure having a plurality of material supporting shelves,said tray structure including means for pivotally supporting saidshelves for rotation about respective axes which parallel thelongitudinal axis of said container,

whereby said shelves may assume either a substantially horizontalmaterial supporting position or a substantially vertical collapsedposition, said tray structure being spaced from that end of saidcontainer which is nearest the condenser portion of said chamber.

6. In a sublimation apparatus having a heating chamber, a substantiallyclosed horizontally disposed cylindrical container removably positionedwithin said chamber, and an elongated tray structure removablypositioned within said container, said tray structure comprising avertically disposed support frame, a plurality of verticaiiy spacedshelves, and hinge means at the inner edges of said shelves forpivotally supporting said shelves from said frame for rotation aboutrespective axes which parallel the axis of said cylindrical container,at least some of said shelves being of suflicient width that their outeredges engage the inner surface of said cylindrical container when saidshelves assume a substantially horizontal position.

7. In a sublimation apparatus, in combination, an elongated horizontallydisposed substantially closed container, said container having anopening extending lengthwise thereof at its top, and an elongatedremovable tray structure disposed within said container, said traystructure comprising vertically disposed end members spaced along thelength of said container, a plurality of horizontally extendingvertically spaced shafts for retaining said end members in spacedrelation, a plurality of material supporting shelves, means forpivotally mounting the inner edges of said shelves on said shafts forrotation thereabout, and at least one horizontally disposed transversesupporting member attached to at least one of said end members forengaging the under surface of at least a pair of said shelves forsupporting said pair in a substantially horizontal position.

8. In combination, a substantially closed horizontally disposedcylindrical container, said container having an opening extending alongits top and parallel to its axis, and an elongated tray structureremovably positioned within said container, said tray structurecomprising a vertically disposed support frame, a plurality of normallysubstantially horizontal shelves, and means for pivotally supportingsaid shelves from said frame for rotation about respective axes whichparallel the axis of said cylindrlcal container, whereby said shelvesmay be rotated to a substantially vertical position so as to etfectivelycollapse said entire tray structure, said tray structure in saidcollapsed condition having over-all dimensions smaller than said openingso that it may be removed from said container through said opening.

References Cited in the file of this patent UNlTED STATES PATENTS870,835 Loew Nov. 12, 1907 964,871 Johnson July 19, 1910 1,304,572Kluchansky May 27, 1919 1,662,070 Lyford Mar. 13, 1928 1,888,996McInerny et al Nov. 29, 1932 1,955,272 Carl et al Apr. 17, 19342,035,453 Betterton Mar. 31, 1936 2,113,230 Ceccon Apr. 5, 19382,258,374 Amati Oct. 7, 1941- 2,289,328 Pechukas July 7, 1942 2,304,463Maier Dec. 8, 1942

1. A SUBLIMATION APPARATUS COMPRISING A CHAMBER HAVING AN ELONGATEDHEATING PORTION AND A CONDENSING PORTION COMMUNICATING WITH SAID HEATINGPORTION, AN ELONGATED REMOVABLE SUBSTANTIALLY CLOSED CONTAINERPOSITIONED WITHIN SAID HEATING PORTION, SAID CONTAINER HAVING ARELATIVELY NARROW OPENING AT ITS TOP EXTENDING ALONG THE ENTIRE LENGTHTHEREOF, AND AN ELONGATED TRAY STRUCTURE REMOVABLY POSITIONED WITHINSAID CONTAINER, SAID TRAY STRUCTURE HAVING A PLURALITY OF NORMALLYSUBSTANTIALLY HORIZONTAL SHELVES FOR SUPPORTING PORTIONS OF A CHARGE TOBE SUBLIMED IN LAYERS IN SAID HEATING PORTION, SAID TRAY STRUCTUREINCLUDING MEANS FOR PIVOTALLY SUPPORTING SAID SHELVES FOR ROTATION ABOUTRESPECTIVE AXES WHICH PARALLEL THE LONGITUDINAL AXIS OF SAID CONTAINER,WHEREBY SAID SHELVES MAY BE ROTATED TO SUBSTANTIALLY A VERTICAL POSITIONAND THE TRAY STRUCTURE MAY THEREAFTER BE REMOVED THROUGH THE OPENING INTHE TOP OF SAID CONTAINER.